The main reason is that the risk of space flight doesn’t justify the marginal (if any) benefit.

According to Wikipedia there was 47,000 tons of high level radioactive waste in 2002. I’m too lazy to look up more up to date numbers. If we launched that all into space on F9 heavy rockets it would take 1,807 launches if all the mass was used for waste. That’s using 26 tons capacity to GTO. We would probably want to put the waste in a really strong container that will probably take up 25-50% of the mass needed so now we are up to about 3000 launches.

Since no rocket system is perfect we have to expect some failures. Let’s assume SpaceX gets a 99.9% reliability schedule that means we blow up 3 rockets on launch, spreading 50-75 TONS of high level radioactive waste all over the planet.

Compare that to just letting it sit there and not bother anyone. It’s far better to spend a fraction of the money of 3000 launches on building insanely strong storage areas and just leaving it alone.